There are many applications in academic, industrial, and medical fields that benefit from devices and methods that are capable of accurately and controllably delivering fluids, such as liquids and gases that have a beneficial effect when administered in known and controlled quantities. Such devices and methods can be particularly useful in the medical field where treatments for many patients include the administration of a known amount of a substance at predetermined intervals.
One category of devices for delivering such fluids is that of pumps that have been developed for the administration of insulin and other medicaments for those suffering from both type I and type II diabetes. Some pumps configured as portable infusion devices can provide continuous subcutaneous medicament injection and/or infusion therapy for the treatment of diabetes. Such therapy may include, e.g., the regular and/or continuous injection or infusion of insulin into the skin of a person suffering from diabetes and offer an alternative to multiple daily injections of insulin by an insulin syringe or an insulin pen. Such pumps can be ambulatory/portable infusion pumps that are worn by the user and may use replaceable cartridges. Examples of such pumps and various features that can be associated with such pumps include those disclosed in U.S. Patent Publication Nos. 2013/0324928 and 2013/0053816 and U.S. Pat. Nos. 8,287,495; 8,573,027; 8,986,253; and 9,381,297, each of which is incorporated herein by reference in its entirety.
Portable infusion pumps for delivering insulin or other medicaments can be used in conjunction with blood glucose monitoring systems, such as blood glucose meters (BGMs) and continuous glucose monitoring devices (CGMs). A CGM provides a substantially continuous estimated blood glucose level through a transcutaneous sensor that estimates blood analyte levels, such as blood glucose levels, via interrogation of the patient's interstitial fluid rather than the patient's blood. CGM systems typically consist of a transcutaneously-placed sensor, a transmitter and a monitor. A CGM system allows a patient or caregiver to insert a single sensor probe under the skin for multiple days. Thus, the patient is only required to perform a single moderately invasive action with a single entry point in the subdermal layer on, e.g., a weekly basis.
Ambulatory infusion pumps typically allow the patient or caregiver to adjust the amount of insulin or other medicament delivered, by a basal rate or a bolus, based on blood glucose data obtained by a BGM or a CGM, and in some cases include the capability to automatically adjust such medicament delivery. Some ambulatory infusion pumps may include the capability to interface with a BGM or CGM such as, e.g., by receiving measured or estimated blood glucose levels and automatically adjusting or prompting the user to adjust the level of medicament being administered or planned for administration or, in cases of abnormally low blood glucose readings, automatically temporarily ceasing or prompting the user temporarily to cease insulin administration. These portable pumps may incorporate a BGM or CGM within the hardware of the pump or may communicate with a dedicated BGM or CGM via wired or wireless data communication protocols, directly and/or via a device such as a smartphone. Such pumps may be particularly important in facilitating patient compliance and improved or more accurate treatment of diabetes. One example of integration of infusion pumps with CGM devices is described in U.S. Patent Publication No. 2014/0276419, which is hereby incorporated by reference herein.
The delivery of insulin or other medicament from a portable infusion pump making use of CGM data necessitates accurate and reliable CGM data output. Some CGM devices are calibrated with blood samples to correlate actual blood glucose data with the CGM readings. However, such calibrations are only done periodically, such as every few days or hours, such as 12 hours, and the longer it has been since a calibration event the more likely the CGM is unreliable to some degree and the more unreliable the CGM is likely to become until the next calibration.
As noted above, insulin or other medicament dosing by basal rate and/or bolus techniques could automatically be provided by a pump based on readings received into the pump from a CGM device that is, e.g., external to the portable insulin pump or integrated with the pump as a pump-CGM system in a closed-loop or semi-closed-loop fashion. With respect to insulin delivery, some systems including this feature can be referred to as artificial pancreas systems because the systems serve to mimic biological functions of the pancreas for patients with diabetes.
However, there are a number of risks in automatically dosing insulin, or other medicaments, based on CGM readings that may be inaccurate or unreliable. For example, a CGM reading or readings may indicate that a user's blood glucose level is high and therefore the pump may automatically deliver a bolus of a medicament such as insulin or increase the basal rate of a medicament such as insulin to lower the user's blood glucose to a target level. If the CGM reading inaccurately indicates that the user's blood glucose level is high, the extra insulin delivered in response may actually lower the user's blood glucose level below a desired target level, possibly to a dangerously low level. This problem may not be detected until the CGM is next calibrated, perhaps not for several hours. Thus, automatically dosing medicaments such as insulin based on CGM readings can have potentially dangerous effects in situations where the CGM readings are inaccurate or unreliable relative to the user's actual blood glucose levels. Similarly, any failure of the CGM sensor, loss of signal or communication between the CGM and the pump, other mechanical or electrical failures with the system or problems with the user's operation of the system or its components, for example, may also be dangerous to the patient.
Thus, a need exists for devices and methods that maintain safe delivery of insulin to a patient in the event of a failure of closed-loop or semi-closed-loop automatic dosing of an insulin pump.